OPERATIVE Flashcards
One reason that the fluoride ion can easily substitute for the hydroxide ion in hydroxyapatite structure is:
A. the fluoride ion and hydroxide ion are oppositely charged. B. the fluoride ion has more valence electrons. C. the fluoride ion is slightly smaller than the hydroxide ion. D. hydroxide and fluoride are from the same chemical family. E. S.mutans acts as a fluoride exchanger.
C. the fluoride ion is slightly smaller than the hydroxide ion:
In topical fluoride application, a fluoride ion substitutes for a hydroxide ion in enamel structure. The resultant fluoroapatite is less susceptible to plaque acids. Two similarities between hydroxide and fluoride help this to occur. One is that they have the same electrical charge (-1). The other is that they are of comparable size, although fluoride is slightly smaller. This means that it is relatively easy for fluoride to fit into the chemical structure formerly occupied by hydroxide. The fluoride ion and the hydroxide ion have the same amount of valence electrons. A differing amount of valence electrons (choice B) would indicate an unequal ionic charge; thus, making it harder to substitute one for the other. Hydroxide and fluoride are not from the same chemical family (choice D), as fluoride is a halogen ion and hydroxide is a polyatomic ion of hydrogen and oxygen. Opposite charges on these two ions (choice A) would make it more unlikely that one would substitute for the other. S. mutans is not directly involved in fluoride exchange (choice E).
Which of the following materials has the GREATEST coefficient of thermal expansion?
A. Composite B. Gold C. Acrylic D. Amalgam E. Tooth structure
C. Acrylic:
One of the reasons that acrylic is not used as a restorative material is its high coefficient of expansion. Acrylic expands and contracts greatly with temperature change, and these changes can be severe within the oral cavity. Since the expansion rate is much greater than that of natural tooth structure, restorations loosen and percolate fluids at the margins. This will ultimately lead to failure of the restoration. One of the major early advantages of composites (choice A) was their reduced expansion coefficient, due in part to the fact that the resin is filled with quartz and glass particles. Gold (choice B) and amalgam (choice D) have expansion coefficients fairly close to tooth structure (choice E). Of the two, gold is closer, but it is sometime cost prohibitive as a common restorative material.
Delayed expansion in amalgam is due to a reaction of:
A. zinc, yielding water vapor. B. mercury vapor, yielding hydrogen. C. mercury, yielding sulfides. D. zinc, yielding hydrogen.
D. zinc, yielding hydrogen:
The major problem with zinc-containing amalgam alloys is delayed expansion. If the zinc-containing alloy contacts water during mixing and placement, a chemical reaction will occur over the next several weeks, where hydrogen gas is formed within the amalgam, causing pressure, discomfort, and increased marginal breakage and corrosion. Therefore, choices A, B, and C are incorrect.
In which tooth should the pulpal floor be inclined lingually during preparation?
A. Tooth 29 B. Tooth 12 C. Tooth 4 D. Tooth 21
D. Tooth 21:
is a mandibular first premolar. In performing operative dentistry on specific teeth, certain anatomic considerations may exist. Before proceeding with an operative procedure, the doctor should examine the preoperative radiographs to identify possible problems. The pulp of the mandibular first premolar follows the anatomy of the tooth. Therefore, it has a very prominent buccal pulp horn and a much smaller lingual. The buccal pulp horn often can be positioned near the center of the tooth, making it difficult to prepare the occlusal portion for restoration. When the occlusal portion is involved, it is recommended that the floor of the preparation be sloped upward from lingual to buccal to help avoid the pulp horn. The pulp horns of tooth 12 (choice B) are typically even, and teeth 29 (choice A) and 4 (choice C) usually have a single, centrally located canal.
Placing a sprue into a wax pattern requires all of the following EXCEPTone. Which one is the EXCEPTION?
A. It should be positioned away from the margins and occlusal contacts. B. It should be wide enough to prevent congealing before the pattern has solidified. C. It should be placed on the bulkiest, noncentric cusp. D. The length should be as long as possible between crucible and wax pattern.
D. The length should be as long as possible between crucible and wax pattern:
A sprue should be positioned to lead molten metal with a minimum amount of turbulence. Because the sprue will eventually be removed, it is important that it be placed in a position that will not compromise the occlusion and final fit of the restoration (i.e., avoiding margins, contact points, functional cusps, etc.), which makes choices A and C incorrect. This means that the sprue should be smooth and funnel into the wax pattern without any sharp turns (choice B). It should also be short between the crucible and the wax pattern and large enough to prevent congealing before the pattern has solidified.
In an amalgam alloy, which of the following constituents is present in the smallest proportion?
A. Mercury B. Silver C. Copper D. Tin E. Zinc
E. Zinc:
The one component that may or may not be found in amalgam alloy is zinc. The typical proportion is usually between 0% and 2%. An alloy containing zinc and contaminated with water during the mixing or condensation stage of the amalgam can exhibit an expansion that starts about 3 to 5 days after placement of the restoration. This delayed expansion will result in a weak restoration. Amalgam alloys usually consist of 40% silver (choice B), 32% tin (choice D), 30% copper (choice C), and the rest are a mixture of trace metals including zinc. Choice A is incorrect.
A 45-year-old female complains of a sharp pain and/or shock in the left side whenever she eats. You suspect a galvanic reaction. Upon clinical examination, what sorts of restorations would you expect to see in contact with each other?
A. Two large amalgams B. A large amalgam and a large composite C. A large amalgam and a gold onlay D. Two gold onlays E. A gold onlay and a large composite
C. A large amalgam and a gold onlay:
Oral galvanic currents occur when there are two or more different metals in contact with, or in opposition to, each other that are bathed in saliva, containing electrolytes. This set-up constitutes an electric cell, similar to that of a battery. When these metals are brought into contact, current will flow through the metal to the pulp, producing a sharp pain or a shock. The key here is that two different metals are required for a galvanic effect. Thus, gold and amalgam can produce this effect. The other answer choices are either between two of the same type of metals (choices A and D) or between a metal and a plastic/composite (choices B and E).
Cavity varnish is composed of:
A. volatile solvent and eugenol. B. copal resin in acidic solution. C. polyacrylic acid in ethanol. D. copal resin in volatile solvent.
D. copal resin in volatile solvent:
Varnish consists of copal resin in volatile solvent (Copalite). When applied, the solvent evaporates, leaving the thin resin behind. The resin coating can seal dentinal tubules and prevent chemical irritation of pulp and can also help seal margins. Eugenol (choice A) is used as a pulpal sedative. Using acidic solution (choice B) with varnish would irritate the pulp and defeat the purpose of the varnish. Polyacrylic acid (choice C) is used in glass-ionomer cements.
Which of the following describes the cavity preparation step that enables the tooth and the restoration to withstand masticatory forces without fracture?
A. Outline form B. Resistance form C. Retention form D. Convenience form
B. Resistance form:
is the shape and placement of preparation walls that best enables both the restoration and the tooth to withstand masticatory forces without fracture.
Establishing outline form occurs when preparation margins are placed in the precise positions they will occupy in the final preparation, with the exception of the finishing of the enamel walls and margins.
Retention form is that which is established by features in the axial design that resist displacement of the restoration.
Convenience form is the final shape of the preparation needed to allow for complete removal of carious tooth structure.
All of the following are TRUE statements about the use of pins EXCEPT one. Which one is this EXCEPTION?
A. Pins should be placed 2 mm into dentin. B. Pins should be placed 2 mm into the amalgam. C. Pins should be placed at least 1 mm from the DEJ. D. Pins are intended only for reinforcing the final restoration.
D. Pins are intended only for reinforcing the final restoration:
Pins do not increase or contribute to the strength of an amalgam restoration. They are intended to help the retention of the amalgam restorative material. Pins do not reinforce the final restoration and may, in fact, provide areas or points of fracture. Pins should ideally be placed 2 mm into the dentin (choice A), 2 mm into the amalgam (choice B), 1 mm from the DEJ (choice C), and not be bent.
Which of the following is NOT a characteristic of a glass-ionomer base material?
A. Good physical properties for a base B. Chemical bond to tooth structure C. Fluoride release D. Anticariogenic activity E. Reliance on mechanical retention in the cavity preparation
E. Reliance on mechanical retention in the cavity preparation:
Glass-ionomer cement can be used for both luting and basing (choice A). It is the only base material that can chemically bond to tooth structure (choice B), even without prior conditioning. This property allows for conservation of tooth structure because you do not have to create retention in a preparation. In addition, glass-ionomer cement is very strong and has anticariogenic activity (choice D). Choice C is incorrect.
Resistance to proximal displacement in a class II amalgam restoration is achieved by:
A. eliminating occlusal dovetail. B. retention grooves placed in the axiobuccal and axiolingual line angles. C. occlusally converging buccal and lingual walls. D. tight contact with the adjacent tooth.
B. retention grooves placed in the axiobuccal and axiolingual line angles:
Resistance to proximal displacement in a class II amalgam is provided by placing grooves in the axiobuccal and axiolingual line angles that extend the height of the axial wall. It is very important not to undermine the enamel. Additional retention is aided by the dovetails (choice A) in the occlusal portion of the preparation. Occlusally converging the buccal and lingual walls (choice C) will help more with occlsual displacement, rather than proximal displacement. Tight contacts (choice D) are important to the health of the gingiva. They are not designed to provide retention to proximal displacement.
An adult patient receives a blow to the anterior maxilla, which moves tooth 8 into a lingually displaced position. There is no radiographic or clinical evidence of fracture. The MOST appropriate treatment for this tooth is:
A. careful observation, let it return to normal, and reposition as the tissues heal. B. to begin endodontic therapy. C. to splint tooth with composite and wire, and take it out of occlusion. D. to take it out of occlusion.
C. to splint tooth with composite and wire, and take it out of occlusion:
Trauma to a tooth that displaces it lingually is usually treated by moving the tooth back into position and splinting it. Splinting keeps the tooth from moving during healing of the bone, and moving it into position helps it to heal in the normal position. Observation alone (choice A) tends to put the tooth more at risk for further occlusal trauma and does not allow it to reposition. Endodontic therapy (choice B) is not indicated until symptoms of irreversible pulpal damage occur. Taking the tooth out of occlusion helps prevent further occlusal trauma; however, by itself (choice D), this treatment is insufficient.
An adult patient receives a blow to the anterior maxilla, which moves tooth 8 into a lingually displaced position. There is no radiographic or clinical evidence of fracture. The MOST appropriate treatment for this tooth is:
A. careful observation, let it return to normal, and reposition as the tissues heal. B. to begin endodontic therapy. C. to splint tooth with composite and wire, and take it out of occlusion. D. to take it out of occlusion.
C. to splint tooth with composite and wire, and take it out of occlusion:
Trauma to a tooth that displaces it lingually is usually treated by moving the tooth back into position and splinting it. Splinting keeps the tooth from moving during healing of the bone, and moving it into position helps it to heal in the normal position. Observation alone (choice A) tends to put the tooth more at risk for further occlusal trauma and does not allow it to reposition. Endodontic therapy (choice B) is not indicated until symptoms of irreversible pulpal damage occur. Taking the tooth out of occlusion helps prevent further occlusal trauma; however, by itself (choice D), this treatment is insufficient.
Which of the following does NOT add to the retention of a class III acid-etched resin restoration?
A. Acid etching B. Adhesiveness of bonding liquid C. Lingual dovetail D. Retention points in dentin
B. Adhesiveness of bonding liquid:
Strictly speaking, composite resin does not adhere to tooth structure. That is, it does not act like a cement, such as polycarboxylate, which chemically adheres to tooth structure. Instead, it physically and mechanically locks into etched spaces in the enamel. Thus, acid etching will add retention in a microscopic way. A dovetail adds retention in a gross macroscopic way, preventing proximal movement of the filling. Retention points also act as little mechanical locks, making the filling harder to move out of position.
Which of the following features can be found in a cavity preparation for a class V amalgam restoration?
A. The outline form should be shaped like a rectangle. B. The mesial and distal walls converge. C. Undercuts are placed in the axial wall for retention purposes. D. The axial wall is uniformly deep into the dentin and is convex.
D. The axial wall is uniformly deep into the dentin and is convex:
Amalgam restorative material can be used to restore a class V cavity that may have been caused by caries, erosion, or abrasion. The axial wall is of even thickness into the dentin and is convex, following the contour of the tooth. The outline form is trapezoidal or kidney shaped, not rectangular (choice A). All of the line angles should be slightly rounded, and the margins should be at 90 degrees to the tooth structure. The mesial and distal walls diverge, not converge (choice B), and undercuts are placed incisally and gingivally but never into the axial wall (choice C).
The addition of small filler particles to composite resin will lead to which of the following results?
A. Improved finishing characteristics and less resistance to wear B. Lower finishing characteristics and less resistance to wear C. Improved finishing characteristics and improved resistance to wear D. Lower finishing characteristics and improved resistance to wear
C. Improved finishing characteristics and improved resistance to wear:
The addition of filler greatly enhances several properties of this material. Filler particles reduce the polymerization shrinkage and the coefficient of thermal expansion and also improve wear resistance, making choices A and B incorrect. In particular, small filler particles (as opposed to larger size) make a composite more finishable, making choices B and D incorrect, and more resistant to wear. Think of large particles making a rough surface even when polished and flaking off more easily. It is important to remember that composite resins are inferior to amalgam restorations in compressive strength and abrasion resistance.
In a Class V gold foil restoration, the mesial and distal walls of the preparation add:
A. resistance for gold compaction and retention. B. resistance for gold compaction but not retention. C. retention, but not resistance for gold compaction. D. neither resistance for gold compaction nor retention.
B. resistance for gold compaction but not retention:
The mesial and distal walls of the Class V gold foil preparation follow the outlines of the tooth surface and thus tend to flare outward. As such, they cannot add to retentive form. The incisal and gingival walls are parallel to each other and perpendicular to the long axis of the tooth. They will add to retention. All walls are used to resist the pressure of gold condensation. It is not required that a wall need to be retentive in order to withstand force. Tooth walls of any type and reinforced matrices both help to withstand condensation force.
Contact areas must be restored to:
A. help prevent recurrent decay. B. help in the retention and resistance of the final restoration. C. provide protection to the gingiva. D. add overall strength to the restoration.
C. provide protection to the gingiva:
Teeth with open contacts may predispose a patient to periodontal problems. Open contacts can lead to food impaction, which in turn injures the papilla and can result in chronic inflammation. Restoration must have the proper retention and resistance form but cannot rely on adjacent teeth to provide this feature. Therefore, the presence or absence of a proximal contact should have no effect on the strength of the restoration because they do not prevent decay or strengthen the final restoration. Their primary purpose is to protect the gingiva.
When an MO amalgam restoration on a maxillary premolar fractures at the isthmus, it is MOST likely due to:
A. insufficient compressive strength of the brand of amalgam chosen. B. insufficient depth of the isthmus. C. insufficient width of the isthmus. D. delayed expansion of the amalgam.
B. insufficient depth of the isthmus:
In the MO preparation for amalgam, the isthmus must be deep enough to resist compressive force. The isthmus is the weakest area of the restoration, being both thin and shallow. The shallowness, in particular, is believed to be responsible for breakage at the isthmus, making choice C incorrect. The preparation includes a bevel at the axiopulpal line angle, both to add amalgam bulk there and to soften the right angle of tooth structure so that it does not act as a sharp wedge into the amalgam. All commercially available amalgams have sufficient compressive strength (choice A). Delayed expansion (choice D) occurs usually when zinc in the amalgam contacts water during placement. This may cause sensitivity of the tooth and weakness in the amalgam but is not the chief cause of isthmus fracture.
The MAJOR function of a cavity varnish when used in a Class I occlusal amalgam preparation is:
A. increasing the marginal seal. B. decreasing temperature sensitivity. C. soothing action on the pulp. D. stimulating action on dentin formation.
A. increasing the marginal seal:
Cavity varnish is best viewed as a liner and is clearly not a base. It has little, if any, thermal protective effect. It can prevent some leakage of amalgam corrosion products into dentinal tubules and minimize discoloration. It also fills microgaps at the margin, reducing sensitivity and recurrent decay. It can also be used under zinc phosphate to reduce acid exposure of the dentinal tubules. A base (zinc phosphate, zinc oxide-eugenol, glass ionomer) would be most effective in reducing temperature sensitivity. Any material containing eugenol (ZOE, etc.) will have a sedative effect on the pulp. Calcium hydroxide would be most effective in stimulating dentin formation.
Which of the following is NOT characteristic of preparations using a glass-ionomer cement?
A. Good physical properties for a base B. Chemical bond to tooth structure C. Fluoride release D. Anticariogenic activity E. Reliance on mechanical retention in cavity preparation
E. Reliance on mechanical retention in cavity preparation:
Glass-ionomer cement can be used for both luting and basing. It is the only base material that can chemically bond to tooth structure, even without prior conditioning. This property allows for conservation of tooth structure because you do not have to create retention in a preparation. Glass-ionomer has an intrinsic release of fluoride that can be recharged in a high fluoride environment. In addition, glass-ionomer cement is very strong and has anticariogenic activity.
The major difference in preparation between porcelain fused to metal crowns and porcelain jacket crowns is the:
A. amount of facial reduction. B. amount of incisal reduction. C. degree of parallelism. D. type of finishing line.
D. Type of finishing line:
PFM and porcelain jacket crown preparations are similar in many ways. In both cases, sufficient reduction is needed for the material (porcelain and metal, metal only or porcelain only). 1.5 to 2 mm is often reduced on facial surfaces. Lingual surfaces may have slightly less reduction if metal is used by itself on the lingual; otherwise, it is similar. Incisal reduction in both cases is similar, enough for clearance and metal/ porcelain or porcelain alone. Degree of parallelism should be similar, as parallel preparations have higher retention. The major difference lies in the type of margin created. PFM crowns have a metal collar, which adapts closely to a gingival bevel on the tooth preparation. Porcelain jackets have a butt-joint margin. This is because porcelain is very fragile when thin and is not therefore cast in shapes to fit bevels. An approximately 1 to 1.5 mm butt-joint of porcelain is used instead.
The failure of pin-retained restorations can occur at several locations. Which of the following is the MOST likely area for failure?
A. Within the restoration B. Interface between restorative material and pin C. Within dentin (dentin fracture) D. Interface between dentin and pin
D. Interface between dentin and pin:
The most common location for failure is between the pin and the dentin. This can occur for several reasons, including selecting the wrong pin drill, using the drill incorrectly, and not stabilizing a pin before bending or cutting it. All of these can affect the pin-dentin interface. Fractures do not typically occur within the restoration (choice A), between the restoration and pin (choice B), or within the dentin (choice C).
Which of the following constituents is a scavenger for oxides and sulfides and is associated with delayed expansion?
A. Silver B. Mercury C. Tin D. Copper E. Zinc
E. Zinc:
Silver mainly functions to provide strength to the restoration.
Tin mainly functions to decrease corrosion of the final restoration.
Copper adds strength to the amalgam alloy and contributes to setting expansion.
Mercury is the principle chemistry agent driving the amalgamation reaction that turns the soft moldable components into a solid restorative material.
Zinc acts as a scavenger for oxides and sulfides and has effects on delayed expansion. If the alloy is contaminated with water during the mixing or condensation phase, it will exhibit delayed expansion. This is caused by the production of zinc oxide and hydrogen gas. The gas will cause the amalgam to expand several days after placement, and expansion could continue for several months. This delayed expansion will result in a weak restoration and discomfort for the patient.
Which of the following is the reason a matrix band for a Class II restoration is placed occlusally above the crown?
A. To prevent the escape of the restorative material during condensation B. To allow overfilling of amalgam C. To determine the contact point D. To restore proper embrasure spaces
B. To allow overfilling of amalgam:
At the occlusal portion, the band should be approximately 1 mm above the occlusal table. This would allow overfilling of the restoration and proper carving to provide the correct functional anatomy. As the band is properly burnished against the adjacent tooth and wedged, this will help prevent the escape of restorative material during condensation (choice A), determine the contact point (choice C), and restore proper embrasure spaces (choice D).
A dental instrument has a blade that forms a right angle with the long axis of the handle. This angle in centigrade degrees is:
A. 25° . B. 50° . C. 90° . D. 100° .
A. 25°:
The degree measurement on operative dentistry instruments is based on centigrade degrees, not on the 360-degree system that we are normally familiar with from geometry. In the centigrade system, the whole circle is 100º (choice D), not 360. A semicircle is 50º (choice B), not 180. Therefore, a right angle (quarter circle) is 25º , not 90 (choice C).
When light-cured composites are compared with self-cured composites, we find that:
A. more air is incorporated into self-cured fillings. B. self-cured composites are easier to shape before curing. C. self-cured materials are contaminated less often. D. setting times can be varied for light-cured composites.
A. more air is incorporated into self-cured fillings:
This question reviews some basics of self-cured composites. While they are currently used less often than light-cured composites, they are still useful and preferred by some practitioners in some cases. They have some disadvantages as compared with the light cured variety: (1) In mixing, air bubbles may get trapped, causing weakness in the restoration; (2) placement is more difficult and shaping may be interfered with as the composite hardens, making choice B incorrect; (3) if rushing, a dentist may contaminate the base, making choice C incorrect, with catalyst or the catalyst with base by placing the mixing stick into the stock jar of base and catalyst the wrong way. Though the set time of a light-cured composite cannot be varied, making choice D incorrect, this is not a problem because the curing can be held off indefinitely until ready. However, note that some variation in setting of a self-cured composite can be controlled by varying the proportion of base and catalyst in the mix. A lower catalyst level results in more working time.
Which of the following should be done when preparing an occlusal cavity on a mandibular first premolar?
A. Prepare one cavity, including all pits and fissures. B. Prepare two separate pits. C. Prepare one or two pits depending on the anatomy and caries. D. Always go the depth of a 330 bur.
C. Prepare one or two pits depending on the anatomy and caries:
The mandibular first premolar has a variety of occlusal forms. If there are two distinct pits, no distinct fissure joining them, and the cavities are small, then two separate pits are advised, making choice A incorrect. This will conserve tooth structure and help retain the strength of the remaining tooth. If the pits are very close, have a deep fissure joining them, or if the excavation brings the pits too close together, then one preparation joining the two pits is preferred, making choice B incorrect. The depth of the preparation (choice D) will always be determined by the extent of caries, not the length of the bur.
Which of the following constituents is present in the smallest proportion in an amalgam alloy?
A. Mercury B. Silver C. Copper D. Tin E. Zinc
E. Zinc:
The one component that may or may not be found in amalgam alloy is zinc. The typical proportion is usually between 0% and 2%. An alloy containing zinc and contaminated with water during the mixing or condensation stage of the amalgam can exhibit an expansion that starts about 3 to 5 days after placement of the restoration. This delayed expansion will result in a weak restoration. Amalgam alloys usually consist of 40% silver (choice A), 32% tin (choice B), 30% copper (choice C), and the rest are a mixture of trace metals including zinc. Choice D is also incorrect.
Water contamination of a zinc-containing amalgam:
A. minimizes creep. B. causes excessive tarnish. C. causes expansion with increased compressive strength. D. can cause postoperative sensitivity.
D. can cause postoperative sensitivity:
Water reacts with zinc in amalgam alloy to produce hydrogen gas, which causes delayed expansion. This delayed expansion may cause discomfort to patients. Creep is a problem with margins, in particular, as the metal deforms over time with occlusal loading. Copper in the amalgam reduces creep. Tarnish is usually caused by the reaction of amalgam with sulfur containing materials, causing sulfide tarnish at the alloy surface. Neither tarnish nor creep are associated with direct patient discomfort. Note that delayed expansion is associated with reduced strength, not greater strength.
